Two-motor control for screw feed machine tool units



Dec., w, i935. A E. J. KINGSBURY @3343 TWO-MOTOR CONTROL FOR SCREW FEEDMACHINE TOOL UNITS Filed July l1, 1932 3 Sheecs-Sheet l E@ w, w35@ E. J.KINGSBURY TWO-MOTOR CONTROL FOR SCREW FEED MACHINE TOOL UNITS Filed Julyv11, 1952 s sheets-sheet 2 @Mm/wmp De@ E@ QBS@ I E KlNGSBURY 2,023,841

TWO-MOTOR CONTROL FOR SCREW FEED MACHINE TOOL UNITS Filed July ll, 19323 Sheets-Sheet 5 /fz M? lll 551/3 www.

Patented Dec. l0, 1935 UNITED STATES TWO-MOTOR CONTROL FOR SCRW` FEEDMACHINE TOOL UNITS Edward Joslin Kingsbury, Keene, N. l1. ApplicationJuly 11, 1932, Serial No. 621,966

20 Claims.

'I'his invention relates to improvements in feeds for machine tool'units, and more particularly concerns a screw feed unit in which twomotors are employed for obtaining different feeding speeds.

One of the features of the present invention is the provision of meansfor controlling the speeds of two motors whereby three or more differentfeeding speeds may be attained.

Another feature of the invention vis the provision of a feedingmechanism employing two constantly rotating motors, which are operatedat different speeds, but always in the same direction, for obtainingvarious feeds of the tool.

Another feature of the present invention is the provision of meanswhereby the main driving motor may be employed in conjunction with anauxiliary feed motor for obtaining varying feeds, by controlling therelative speeds'of the two motors.

Further features of the invention willI appear in the course of thefollowing specication and claims, in which an illustrative form ofconstruction of the device is shown, and in which:

Figure 1 is a side elevation of a machine and tool unit according to thepresent invention.

Figure 2 is a vertical longitudinal section through the same.

Figure 3 is a transverse vertical section, on a larger scale,substantially on line 3-3 of Figure 2.

Figure 4 is a vertical longitudinal section, on a larger scale than thatof Figure 2, showing the nut and screw feed elements.

Figure 5 is a circuit diagram of the manner of connecting the motors.

In these drawings, the machine tool unit is illustrated as having a baseB having a xed bracket M extending therefrom to support an auxiliaryfeed motor A having a horizontal shaft. A sliding tool head K has aplatform for supporting the main motor R and is provided with a head Hfrom which tool spindles S project. Feeding is accomplished by therelative sliding movement of the tool' structure K and motor R withrespect to the base B, the feeding of the tool to the work occuring by amovement toward the left in Figures 1 and 2, and the return of the toolfrom the work being accomplished from the left toward the right in thesefigures.

The main motor R (Figure 2) has a horizontal shaft I 0 provided with asmall gear I which is in mesh with a large gear I2 carried by anauxiliary shaft I3 having a small gear 4 in mesh with a large gear |5 ona tool driving shaft ,I6 a' gear |'l in mesh with a tool gear I8 mountedon a tool spindle S. Similar driving gears are provided, but not shown,in the usual way for driving the other tool spindles S.

The large gear I2 is likewise in mesh with a 5 gear 20 mounted on aspindle 2| carried by bearings 22 in the head K and including at itsrear end a right-hand threaded portion 23 which engages with aninternally threaded and externally conical nut 24. This spindle 2|extends through 10 an upwardly projecting bracket 25 of the bed B sothat the smooth portion of the spindle is journaled therein duringmovement of the tool carryingdportion K with respect to the bed B asaforesai The auxiliary motor A has its horizontal shaft 30 provided witha gear 3| meshing with a gear 32 on an idler shaft 33 journaled in anupstanding portion of the base B. A second gear 34 on the idler shaft 33is in mesh with a nut driving 20 gear 35 xed on a hollow shaft 36 whichextends forwardly surrounding and in telescoping relationship with thethreaded portion 23 of the spindle 2|, and provided at its front with aninternally conical collar 3l which fits the external 25 conical surfaceof the nut 24 (Figure 4). A plunger sleeve 38 is slidable over thethreaded portion 23 and within the Ihollow shaft 36, being urgedconstantly toward the left in Figure 2 by -a coil spring 39 which reactsagainst one race 30 40 of .a ball-bearing having a second race 4|mounted around a reduced end of an adjusting pin 42, which asv indicatedin Figure 2 may move axiallyby the adjusting screw 43. The hollow shaft36 is carried by ball-bearings 44 in the bed B. 35

Laterally projecting (Figures 1 and 3) from the tool structure K is askirt having a T-groove 5| in which may be adjusted and clamped thethree dogs 52, 53 and 54.

Dog 52 cooperates, at the end of the forward 40 feeding movement of thetool structure, with a switch arm of spring switch 56. Dog 53 cooperatesduring the forward feeding movement at a point corresponding to a closeapproximation of the tool to the work, on a gravity-held pivoted 45finger 5l of a switch arm 58 of spring switch 59. Dog 54 cooperates atthe end of the rearward or withdrawal feeding movement with the arm of aspring switch 6|.

I'hese switches 56, 59, and 6| are connected 60 to the main motor R andto the auxiliary motor A in any desired manner for the purpose ofaccomplishingv the differential speed control of these motors in propersequence.

An illustrative manner of connecting these 55 motor switches and motorsthree-phase source nais and main conductors is joined by the branchphase conductors 8| to contacts of the two three-pole high" speedswitches 82 which may be closed by a solenoid 83, and to the contacts ofthe three-pole low speed switch 84 which may be closed by the solenoid85. Phase conductors 86 lead from the switch 83 to the high speedwindings 81 of the large motor R, while phase conductors 88 lead fromthe switch 84 to the low speed motor R.

The branch phase conductors 90 similarly lead to the three-pole highspeed switch 9| which may be closed by a solenoid 92 and to a threepolelow speed switch 93 w 'ch may be closed by the solenoid 94. Phaseconductors 95 lead from switch 9| to high speed winding 96 of theauxiliary motor A; while conductors 91 lead from switch 93 to the lowspeed winding 98 of this auxiliary motor A. Y

The switch 56 includes a bridge |00 normally engaging upper contacts |0|and movable by dog 52 to close lower contacts |02, this switch beingopened again by a spring |03 when the dog leaves the arm 55.

The switch 59 similarly includes a bridge |04 for normally closing theupper contacts |05, and being actuated by the dog 53 toclose lowercontacts |06, and being opened again by spring |01 when the dog 53 nolonger depresses the pawl 51 and arm 58 as aforesaid The switch 6|includes two mutually insulated bridges, of which the upper bridge |08normally closes contacts |09, while the lower bridge ||0 normally closescontacts III. Upon actuation of the switch by the dog 54, these normallyclosed contacts areopened and the lower bridge ||0 may close a circuitthrough the lower contacts ||2. When the dog 54 leaves arm 60, the partsof switch 8| are moved to the upper position (shown in full lines inFigure 5) by a return spring ||3.

A hand-starting switch I4 may be manually operated to momentarily closecontacts ||5 by a bridge H6. The closure of the hand-starting switch ||4establishes a circuit from the righthand main conductor 80 by busconductor |20 to one contact H5, through the bridge ||6 to the othercontact |15, and by conductor |2| to contacts at switch 9|, and thenceby a switch bridge 9|a and conductor |22, solenoid 92 and conductor |23back by the lower branch conductor 90 to the left-hand main conductor80. The energization of solenoid 92 thus produced causes a closure ofswitch 9| so that current may flow through conductors 90, 95 andenergize the high speed winding 96 of the auxiliary motor A. As theswitch closes, its bridge 9|a opens the circuit through conductor |2|and establishes a circuit closing relationship with conductor |24, thisbeing supplied with current from bus conductor |20, through the normallyclosed contacts' |0| of switch A56. The auxiliary motor thus begins torun at high speed.

' Meanwhile it will be understood that the main R is bein" supplied withcurrent through switch 84 which has been closed by current ilowing fromthe bus conductor |20 to the lower contacts |I2 of switch 6| whenclosed, by conductor |36 to the switch contacts and bridge 84a andthence through the solenoid 85 back to a main conductor 89; and is heldclosed by a similar circuit through the upper contacts |05 of switch 59.

is shown in 5 where a connected to switch termiwindings 89 of this largeat 1800 and 900 R. P. M.,

regarding slip) easily attainable with 60 cycle conductor |25, the othercontacts oi switch 84. and its bridge 84a, so that motor R is moving atlcw speed.

Ir switch 59 is now depressed, the current which has been flowingthrough the closed contacts |05 and conductor |25 is now broken so thatswitch 84 immediately opens. The movement of the switch 59 likewisecloses a circuit from bus conductor |20 through the closed con'- tacts|06 and conductor |26 which is in circuit closing relationship withcontacts and bridge 82a of switch 82 so that solenoid 83 is energizedwith a return of the current by conductor |21 to the left-hand mainconductor 80. The high speed switch 82 isthus closed and the high" speedwinding 81 of the main motor R is energized. As the switch 82 closes,its bridge 82a opens the circuit through conductor |26 and establishes acircuit by conductor |28 which is being supplied with current throughthe closed contacts of switch 6| from the bus conductor |20, thus cre'ating a holding circuit for solenoid 83.

When switch 56 is depressed, the holding circuit from bus conductor |20and contacts |0| by conductor |24 toY bridge 9|a is opened, and solenoid92 is de-energized so/that switch 9| opens. The same movement of switch56 closes contacts |02,so that a circuit is established from busconductor |20 by conductor |29to the bridge 93a of switch 93 and thencethrough solenoid 94 and conductor |03 back to the left-hand mainconductor 80. This energizes the solenoid 94, closes switch 93 andenergizes the"low speed winding 98 of the auxiliary motor A. Themovement of the switch 93 opens the circuit at bridge 93a with respectto conductor |29 and esta lishes a holding circuit by conductorY |3I andthe contacts |09 of switch 6l.

When switch 6| is depressed, the holding circuit through contacts |09and conductor |3| is opened, so thatY solenoid 94 is de-energized, andthe auxiliary motor A cornes to a standstill. The holding circuitthrough contacts and conductor |28 is opened, and solenoid 83 isdeenergized, and the main motor R passes from high speed. The movementof switch 6| however also 'closes a circuit through contacts ||2 andconductor |36 which energizes solenoid 85 and closes the low1 speedswitch 84 for the main motor, which upon movement displaces its bridge84a to establish a holding circuit by cond uctor |25 and contacts |05\fswitch 59. The partsv have now returned to the initial position, withauxiliary motor A at a standstill. ready to be started again by closingthe hand-starting switch ||4.

The invention will now scribed as operating with be illustratively dethe motors operating which are speeds (disalternating current motors.

In operation, the motors are connected to a source of current by closingthe main switch to main conductors 80. When the tools are entirelywithdrawn from the work, the tool structure K is in its right-handposition (Figures 1 and 2) and dog 54 has moved switch lever .60 tobring the auxiliary motor A to a standstill. The switch 6| has likewisebeen operated to bring the main motor R to a speed of 900 R. P. M. sothat this motorV acts through gears |||220 to drive spindle 2| and at aspeed of 450 R. P. M. Owing to the threading of the portion 23 ofspindle 2|, it tends to force the nut 24 toward the left, and the nut 24is drawn, with the assistance of the spring 39, into tight contact withcollar '31: and motorfR may drive the' auxiliary motor A, which latteris now disconnected from the source.

To start a cycle, the operator presses a button ||4, which causes a iiowof current through the high speed windings of the auxiliary motor Awhich brings the motor to a speed o1' 1800 R. P. M. Thiskmotor nowdrives the hollow shaft 36 through the gears 3l-32, 34-35 at a speed ofsay 920 R. P. M. This movement of the hollow shaft 36 is transmitted tocollar 31, and the latter now turns at a speed greater than the speed ofthe threaded portion 23 of spindle 2|, and in the same directiontherewith. The collar 31 therefore engages the nut 24 and causes thelatter to turn and produce a feeding movement of the spindle so that thelatter is moved toward the left in Figures 1, 2, and 4. This movement isdetermined by the pitch of the threaded portion 23 and by the speeds andgear ratios. The

spindle 2| is revolving at 450 R. P. M., and thenut 24 is revolving at920 R. P. M., so that the relative rotation of the two parts as theytravel in the saine angular direction is 470 R. P. M.: and with thefive-pitch screw 23, there is a rapid forward initial feeding of thetools at a speed of 94 inches per minute.

As soon as the dog 53 encounters the pawl 51, it operates switch 59 toeiect delivery of ,current to the main motor R, so that the latter isnow driven at 1800 R. P. M., and thus through the gears in head K causesthe tools to be driven at maximumspeed as determined by other drivinggears, and causes also a rotation of spindle 2| in the same directionasbefore, but at 900 R. P. M. The auxiliary motor A continues to move ata speed of 1800 R. P. M. and the hollow shaft 31 and nut 24 are rotatedat 920 R. P. M. The differential in the two speeds is now 20 R. P. M.,so that the tools are fed forward, while revolving at their own highspeed, with a feed of four inches per minute. 'I'his speed may be variedas desired by exchanging gears 3|, 32, 34, and 36 for other gears` todetermine this ratio, but in each instance it is necessary that thehollow shaft 36 be driven by auxiliary motor A at a speed higher than900 R. P. M. in this illustrative example of construction.-

'Ihe tools now operate upon the work until the dog 52 encounters switchlever 55 and actuates switch 56 to open the circuit which has beensupplying the auxiliary motor windings with current for driving it at1800 R. P. M. and to connect the aux'liary motor A for rotation at 900R. P. M. The hollow shaft 36 and nut 24 are then revolved at a speed of460 R. P. M. and still in the same direction as the movement of thespindle 2|. The relative speeds of the nut 24 and the screw 23 is then440 R, P. M., so that the spindle in overrunning the nut 24 produces apositive return or withdrawal of the tools from the work while 'the'tools are still revolving at their own high rate of speed, this returnor backward feed occurring in the illustrative example at the rate of 88inches per minute.

As the dog 53 encounters the pawl 31, it rocks this pawl but does notactuate the switch lever 58 or switch 59.

v Ultimately, the dog 54 encounters the switch lever 60 and actuatesswitch 6| asdescribed above, but de-energizes the auxiliary motor A, andbrings the main motor R to a speed oi.' 900 R. P. M.

It will be noted'particularly that the driving of the tools whileengaged with the'work is accomplished at the higher speedof the mainmotor R and that, while the machine is idling between operations, thismotor is turning at low speed. 'I'he initial energization b'y closingbutton ||4 merely produces a starting pulse of cur- 5 rent throughthe'small auxiliary motor A. At the changing of speeds accomplished byswitch 59, the larger motor is building up speed, but since this largermotor isgnot'then engaged in,v

driving the tools, the total demand on the line 10.

is not severe. It is thus apparent that the heavy current normallyrequired for starting motors is offset by having the main motor R alwaysre- When the tools engage the work, the additional '.6

load tends to cause'the twomotors to slow down and the amount ofvslippage in the motors thus engendered will vary with the load. Themotor A tends to revolve the end at too great a speed and hence to forcethe tools forward with too :l0 great a feed. The' extra resistance,however, tends to slow this motor A so that the nominal feed isafforded, as controlled by change gears 3| to 36. 'I'he difference inspeeds of the motors at different slippage thus counterbalances itself.35 In order to protect the tools against excessive feed even under suchconditions, the screw 43 may be adjusted to give a proper amount ofcompression to spring 39 so that the nut 24 will slip at a desiredresistance imposed by the work upon 40 the tool.

During the forward feeding of the spindle, i. e. during the leftwardmovement of the tool structure K, any opposition to the regular feedingof the tools, over and above a predetermined amount, 45 results in thepressure of the nut 24 toward the right in Figures 2 and 4, so that thenut becomes disengaged from collar 31 and is no longer driven thereby.The device thus operates as a sensitive feeding structure for the tools,the feeding being determined by the action ofthe coil spring 39, and' asthe resistance is overcome, this coil spring 39operates to advance thetool structure K until the end 24 is again driven by the collar 31. Thispredeterrnination of the pressure for release, and hence thesensitiveness of the feeding may be regulated by adjusting the screwv43.

It is obvious thatthe invention is not limited solely to the form ofconstruction, nor to the dimensions of parts or speeds shown ordescribed, but that it may be employed in many ways within the scope ofthe appended claims. 1

Having thus described the invention, what I claim as new and desire tosecure by Letters Patent, is:

1. A drilling unit including a drill, a frame, a drill supporting bodyreciprocable relative to said frame, a first driving motor mounted onsaid body,

a second driving motor mounted enl said frame, means for continuouslyactuating said motors for rotation in the same direction atlsuccessively different speeds, means for connecting said motors to theframe and body and to one another whereby the motors move the body withrespect to the frame, a iirst limit switch yfor controlling the speed ofmovement of said second motor at a predetermined limit of feeding of thedrill to the Work, a second limit switch for controlling the speed ofmovement of said first and second motors upon a predetermined withdrawalmovement of the drill with respect to the work, a third limit said bodyand held against axial movement relative thereto, a first motor forrotating said spindle and screw,'a nut on said screw, a collarsurrounding said screw and held against axial movement relative to saidframe, a spring connected to the nut to move the nut into engagementwith said collar, a second motor mounted on the'frame for rotating saidcollar in the same direction as said screw, and means controlled by theposition of the body relative to said frame for controlling the relativespeeds of said motors.

3. A machine tool unit for a tool operative upon feeding movement,including a frame, a tool supporting body reciprocable relative to saidframe, a screw member and a nut engaged with the screw member, a collarmember adapted to frictionally engage said nut, one said member beingjournalled in and held against axial movement relative to said frame andthe other said member being journalled in and held against axialmovement relative to said body, independent devices for rotating saidmembers, means controlled by the position of the body relative to saidframe for controlling the relative speeds of said devices, resilientmeans for holding said nut and collar in engagement, and means forvarying the action of said resilient means.

4. A drill unit Aincluding a frame, a drill spindle, a body forsupporting said spindle and reciprocable relative to said frame, a screwjournalled in said body and held against axial movement relativethereto, a first motor for rotating said spindle and screw, a nut onsaid screw, a sleeve surrounding said screw and bearing against saidnut, a hollow shaft surrounding said sleeve and journalled in and heldagainst axial movement relative to said frame, a second motor forrotating said hollow shaft, means on said shaft for engagement with saidnut, a spring engaged with said sleeve for pressing said nut intoengagement with said nut engaging means, externally accessible means forvarying the action of said spring, and means controlled by the positionof the body relative to said frame for controlling the relative speedsof said motors.

5. A machine tool unit for a tool operative upon feeding movement,including a frame, a tool supporting body reciprocable relative to saidframe, a screwA memberland a nut member, one said member being connectedto said frame and the other to the said body, separate electric motorsas sources of power for rotating said members constantly in the samedirection, means controlled by the movement of saidbody into differentpositions relative to said frame for controlling the relative speeds ofsaid` motors whereby to produce cyclic feeding and withdrawal movementsof the body without stopping or reversing said motors, said controllingmeans including devices operating to control the motor speeds forproducing in each cycle a rapid forward traverse, a. slow working feed,and a withdrawal traverse, and a device for actuating said control meansfor 5 initiating a new cycle.

6. A machine tool unit for a tool operative upon feeding movement,including a frame, a tool supporting body reciprocable relative to saidframe,

a screw member and a nut member, one said member being connected tosaid'frame and the other to the said body, separate electric motors assources of power for rotating said members constantly in the samedirection and individually located on said frame and said body, a toolspindle on said body connected for drive by the electric motor mountedon said body, means controlled by the movement of said body intodifferent positions relative to said frame for controlling the relativespeeds of said motors whereby to produce cyclic feeding and withdrawalmovements of the body without stopping or reversing said motors, saidcontrolling means including devices operating to control the motorspeeds for producing in each cycle a rapid forward traverse, a slowworking feed, and a withdrawal traverse, and a device for actuating saidcontrol means for initiating a'new cycle.

7. ,A machine tool unit for a tool operative upon feeding movement,including a frame, a tool-supporting body reciprocable relative to saidframe,

a rotatable screw member and a rotatable nut member, one said memberbeing connected to said frame and the other to the said body, a sourceof power located on said frame ,for continuously driving the said memberwhich is connected tothe frame in one direction and at varying speeds, a

' second source of power located on the body for driving the said memberwhich is connected to the body in the same direction and at varying 4 0speeds, a tool spindle on said body connected for drive by said secondsource, means controlled by the movement of said body into differentpositions relative to said frame for controlling the relative speeds ofsaid sources whereby to produce cyclic feeding and withdrawal movementsof the body Without stopping or reversing said sources, said controllingmeans including devices operating to control the speeds of said sourcesfor producing in each cycle a rapid .forward traverse, a slow workingfeed, and a withdrawal traverse, and a device for actuating said controlmeans for initiating a new cycle.

8. A machine tool unit for a tool operative upon feeding movement,including a frame, a tool supporting body reciprocable relative to saidframe, a screw member rotatable in and axially immovable relative tosaid body, a nut member rotatable in said frame, an electric motor forcontinuously rotating said screw member in one direction and at varyingspeeds, a clutch engageable with said nut member, resilient means toforce said clutch and nut member into engagement and operating when thebody is detained for permitting release of the clutch engagement C5 byrelative axial movement of said clutch and nut member, a second electricmotor for rotating said clutch in said direction and at varying speeds,and means controlled by the movement of said body into differentpositions relative to said frame gior controlling the relative speeds ofsaid devices whereby to produce feeding and withdrawal movements of thebody without stopping or reversing said devices.

9.-A drill unit including a frame, a body reciprocable relative to saidframe, an electric driving motor on said body, a drill spindle on saidbody and rotated by said motor, a screw rotatable in and axiallyimmovable relative to said body, driving means connecting said motor andsaid screw to rotate the same continuously, a nut on said screw, meansjournalledon said frame including friction devices for frictionallyengaging and rotating said nut and including a second electric motor onsaid frame, means controlled by the position of said body relative tosaid frame for cyclically controlling the relative speeds of said motorswhereby to produce feedingl and withdrawal movements of the body withoutstopping or reversing said motors and for detaining' said body in awithdrawn position relative to the frame with slippage of said frictiondevices, and manually operable means for actuating said controllingmeans to initiate a cycle.

10. A machine tool unit for a tool operative upon feeding movement,including a frame, a tool supporting body reciprocable relative to saidframe, two separate electric motors of which one is located on the frameand the other on the body, means for controlling the speeds of actuationof said motors and maintaining them continuously in rotation in the samedirection and including a set of at least three control members and aset of control actuating members for moving said control members, one of said sets being mounted on said frame and the other set on said body,and means for connecting said motors to the frame and body and to oneanother whereby the motors are controlled by the interaction of saidmembers for producing cyclically forward movements at different ratesand withdrawal movements of said body relative to saidl frame, saidconnecting means including a friction device which permits slippagelwhen the body is in withdrawn position relative to said frame, anddevices interconnecting the same'with said controlling means and controlmembers for initiating a cycle.

11. A machine tool unit for a tool operative upon feeding movement,including a frame, a tool supporting body reciprocable relative to saidframe, two separate driving devices of which one is located on, theframe and the other on the body, a tool spindle on said body connectedfor drive by the driving device on said body, means for controlling thespeeds of actuation of said devices and maintaining them continuously in-rotation in the same direction and including a set of at least threecontrol members and a set of control actuating members for moving saidcontrol members, one of said sets being mounted on said frame and theother set on said body, and means for connecting said devices to theframe and body and to one another whereby the devices arev controlled bythe interaction /of said members for producing cyclically forwardmovementsat different rates and withdrawal movements of said bodyrelative to said frame, said connecting means including a frictiondevice which permits slippage when the body is in withdrawn positionrelative to said-frame, and devices interconnecting the same with saidcontrolling means and controhmembers for initiating a cycle.

12. A machine tool unit for a tooloperative upon feeding movement,including a frame, a tool supporting body reciprocable relative vto saidframe, two independent electric driving motors and means for controllingthe speeds of'actuation of the same and maintaining them continuously inrotation in the same direction and including a set of at least threecircuit control members mounted on the frame, and a set of controlactuating members fixed to the body for moving said members atpredetermined relative 5 l positions of said body and frame, circuitmeans connecting said control members and moto'rs, and means forconnecting said motors to the frame and body and to one another wherebythe electric motors are controlled by the interaction of said membersfor producing cyclically feeding movements at different rates andwithdrawal movements of said body relative to said frame, saidconnecting means including a friction device which permits slippage whenthe body is in withdrawn position relative to said frame, and devicesinterconnecting the same with said controlling means and control membersfor initiating a cycle. 13. A machine tooldunit for a tool operativeupon feeding movement, including a frame, a

tool supporting body reciprocable relative to said frame, a rstelectricdriving motor mounted on said body, a second electric drivingmotor mounted upon said frame, means for continuously actuating saiddriving motors in the same di- 25 rection, a screw member and a nutmember engaged therewith, one said member being supported on said bodyand the other said member on said frame, said body supported memberbeing connected for continuous actuation by said first driving motor,and said frame supported member being connected for actuation by, saidsecond driving motor, first and second limit members mounted on saidframe, a third limit member mounted on said frame, means mounted on saidbody for actuating said rst and second limit members at the ends ofpredetermined feeding and withdrawal movements of the body relative tothe frame and for actuating said third limit member ata predeterminedintermediate point of the feeding movement, and means for connectingsaid electric motors to the frame and body and to one another wherebythe motors are controlled by the interaction of said members forproducing feeding movements at different rates and withdrawal movementsof said body relative to said frame without stopping or reversing saiddriving motors.

14. A machine tool unit for a tool operative upon feeding movement,including a` frame, a .tool supporting body reciprocable relative tosaid frame, a rst electric driving motor mounted on said' body, a secondelectric driving motor mounted upon said frame, means for continuouslyactuating said driving motors in the same direction, a screw member anda nut member engaged therewith, one said member being supported 'on saidbody and the other said member on said frame, said body supported memberbeing connected for continuous actuation by said 30 first driving motor,and said frame' supported member being connected for actuation by saidsecond driving motor, a rst limit member on Hsaid frame connected tosaid second driving mo- 6 predetermined positions of said body inrespect to said frame whereby to produce successively a rapid forward, aslow forward, and a rapid reverse feeding movement without stopping orreversing said driving motors. Y

15. A machine tool unit for a tool operative upon feeding movement,including a frame, a-

tool supporting body reciprocable relative to said frame, a screw memberand a nut engaged with 10 the screw member, a collar member adapted tofrictionally engage said nut upon axial movement of the latter, yieldingmeans for maintaining such engagement, one said member being journalledin and held against axial movement relative to said frame, and the othersaid member being joumalled in and held against axial movement relativeto said body, separatev electric motors for continuously rotating saidmembers in the same direction, and means controlled by the movement ofthe body into different positions relative to said frame for selectivelyenergizing the motors for different relative speeds, whereby the membersinterengage at the limit of return movement and a slippage occursbetween 'said nut and collar member for permitting the continuedrotation of both said motors.

16. A machine tool unit for a tool operative upon feeding movement,including a frame, a tool supporting body reciprocable relative to saidframe, a screw member and a nut engaged with the screw member, a collarmember adapted to frictionally engage said nut, one said member beingjournalled in and held against axial movement relative to said frame andthe other said member being journalled in and held against axialmovement relative to said body, independent electric ymotors forcontinuously rotating said members in the same directionfV and meanscontrolled by the position of the body 40 relative to said` frame forcontrolling the relative speeds of said motors, means for4 limiting themovement of said body relative toV the frame so that the continuedrelative rotative movement of the members causes the nut member to. moveaxially relative to said collar member and a slippage occurs betweensaid nut and collar member for permitting the continued rotation of bothsaid motors, and means operating between the nut and collar members formoving the same into engagement.V y

17. A machine tool unit for a tool operative upon feeding movement,including a, frame, a tool supporting body reciprocable relative to saidframe, a screw member and a nut engaged with the screw member, acollar'member adapted to frictionally engage said nut, one/said memberbeing journalled in and held, against axial movement relative to saidframe and the other said member being journalled in and held againstaxial movement relative to said body, independent electric motors forcontinuously rotating said members, means controlled by the position Cof the body relative to said frame for controlling the relativespeeds ofsaid motors, means for limiting the return movement of said bodyrelative to the frame so that the continued rotative movement of themembers causes the nut member to move'axially relative to said collarmember, and resilient means for normally holding said nut and collarmember in engagement whereby the axial relative movement of the membersat the limit of return movement causes a release of the frictionalengagement and a slippage between said nut and collar member forpermitting the continued rotation of both said motors.

18. A machine tool feeding unit consisting of a frame, a tool supportingbody reciprocable relative to said frame, a differential feeding mecha-10 nism consisting of two cooperative rotatable feeding membersconnected individually to said frame and said body, two variable speedelectric motors, Aeach motor being connected to one of said rotatablefeeding members for driving the 15 same, circuit means including controlswitches connected to said-motors for energizing the same for rotationin the same direction but at different ratios of relative speed wherebydifferent rates of feed in either forward or reverse direc- 20 tions maybe obtained, means controlled by the movement of said body intodifferent positions relative to said frame for operating the controlswitches to produce cyclically rapid forward, slow forward and returnmovement of the body, and 25 manual means for operating the controlswitches to start a cycle.

19. A machine tool feeding unit consisting of a frame, a tool supportingbody reciprocable relative to said frame, a screw member and a 30 nutmember, one said member being connected to said frame and the other tosaid body, one electric motor for driving said screw member constantlyin one direction and a second electric motor for driving said nutconstantly in the same 35 direction, circuit means including controlswitches connected to said motors for energizing thesame for rotation inthe same direction but at different ratios of relative speed wherebydifferent feed rates may be obtained, means controlled by 40 themovement of said4 lpdy into different positions relative to said framefor operating the control switches to produce cyclically rapid forward,slow forward and return movements of the body, and manual means foroperating the control 45 switches to start a cycle.

20. A drill unit adapted for single cycle operation, including a frame,a body reciprocable relative to said frame, a screw member and a nutmember, one said member being connected to 50 said frame and the otherto said body, one electric motor connected to said screw member foroperation' in one direction onlyanda second electric motor connected tolsaid nut member for operation in the same direction only, and circuit imeans including electrical controls for energizing the motors each formovement in a single direction and at varying relative motor speedswhereby different rates of feed and a cycle of movement of the body inforward andk reverse 60 directions maybe .obtained and for de-energizingone motor, the other motor being operative during such de-energizationto drive both screw and nut'members at the same speed for providing a.

dwell in the feed, and lalsa means for operating said electric controlsto re-energize said one motor to restart a cycle of movement following`a dwell.

EDWARD JOSLIN KINGSBURY.

